JPH06326089A - Method for forming element isolation structure - Google Patents

Abstract

PURPOSE:To improve yield in a method for forming an element isolation structure. CONSTITUTION:A pad oxide film 12, an oxidation-resistance film 11, and fine particle silicon film 13 consisting of amorphous silicon or crystallitic silicon are successively formed on a silicon substrate 11. A resist 15 defining an element formation region 16 is pattern-formed on an oxidationresistance film 14, The silicon 13 is partially subjected to patterning using the resist 15 as mask (Fin. 2(a)). After the resist 1 is eliminated, selective heat treatment using the oxidation-resistance film 14 as a mask is performed, thus allowing a field oxide film 17 to grow (Fig. 2(b)). Therefore, no recessed and projecting parts are formed on the surface of a bird's beak 18, thus preventing an electrode material from remaining at the bird's beak and eliminating the short-circuiting of the gate electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming an element isolation structure for isolating an element formation region by selectively growing a field oxide film on the surface of a semiconductor substrate.

[0002]

2. Description of the Related Art Conventionally, as a method for electrically separating a plurality of elements formed on a semiconductor substrate, a so-called LO is used.
The COS (Local Oxidation of Silicon) method is widely adopted. In this LOCOS method, a pad oxide film is formed on a silicon substrate, and a silicon nitride film defining an element forming region is patterned on the pad oxide film.
By thermally oxidizing the surface of the silicon substrate using this silicon nitride film as a mask, the pad oxide film in the portion protruding from the silicon nitride film is selectively oxidized, and as a result, a field oxide film grows around the element formation region. . This field oxide film achieves isolation between device formation regions.

However, in the LOCOS method, the field oxide film bites like a bird's beak from the edge portion of the silicon nitride film used as a mask and grows laterally, so-called bird's beak occurs. in this way,
The occurrence of bird's beaks means that the area of the element isolation region, that is, an inactive region, increases correspondingly. Therefore, the area of the element formation region is substantially reduced, which is a major obstacle to the realization of ultra-high integration.

In order to solve the above problem, a method of forming an element isolation structure called a LOPOS method has been proposed. The element isolation technique based on the LOPOS method is shown in FIGS. In the LOPOS method, first, as shown in FIG. 4A, the pad oxide film 2 is formed on the surface of the silicon substrate 1, and then as shown in FIG. 4B, the CVD (Chemical
The polysilicon film 3 is formed on the pad oxide film 2 by the Vapor Deposition method. Further, as shown in FIG. 4C, a silicon nitride film 4 is formed on the polysilicon film 3. An element formation region 8 is formed on the silicon nitride film 4.
A resist 9 that defines is patterned.

Next, as shown in FIG. 5A, the silicon nitride film 4 in the portion protruding from the resist 9 is etched using the resist 9 as a mask. As a result, the silicon nitride film 4 selectively remains on the element formation region 8. At this time, the polysilicon film 3 is also etched to about half the initial film thickness. Then, the silicon substrate 1 is thermally oxidized using the remaining silicon nitride film 4 as a mask. Then, as shown in FIG. 5B, the field oxide film 5 grows by selectively oxidizing the portion of the polysilicon film 3 and the pad oxide film 2 that protrude from the silicon nitride film 4. At this time, since oxygen does not quickly permeate the polysilicon film 3 immediately below the silicon nitride film 4, the polysilicon film 3 serves as a barrier and the field oxide film 5 does not grow much laterally. That is, the bird's beak 7 does not extend into the element forming region 8 for a long time. Then, Fig. 5
As shown in (c), the silicon nitride film 4, the polysilicon film 3 and the pad oxide film 2 on the element formation region 8 are removed, and the element formation region 8 separated by the field oxide film 5 is formed.

[0006]

According to the LOPOS method, a field oxide film having a short bird's beak can be formed, so that it is not necessary to enlarge the element formation region more than necessary, and it is possible to contribute to the realization of ultra-high integration. However, the LO
In the element isolation structure obtained by the POS method, it may cause a short circuit of a gate electrode formed in a later step, and the yield may deteriorate. In the LOPOS method, as shown in FIG.
As shown in FIG. 5, the polysilicon film 3 is used as a barrier for suppressing the lateral growth of the bird's beak 7 of the field oxide film 5. The polysilicon film 3 has large particles, and the field oxide film 5 is thermally oxidized. Grows,
The bird's beak 7 is grown by oxidation along the grains of the polysilicon film 3. Therefore, as shown in FIG. 7, irregularities are formed on the surface of the bird's beak 7 and craters 7a are generated. When an electrode material such as polysilicon is deposited in this state and the gate electrode is patterned, the electrode material remains in the crater 7a generated in the bird's beak 7 and causes a short circuit of the gate electrode.

In view of the above, it is an object of the present invention to provide a method for forming an element isolation structure capable of suppressing the generation of craters in bird's beaks of a field oxide film, eliminating a short circuit of a gate electrode, and improving the yield. .

[0008]

A method of forming an element isolation structure according to the present invention comprises a step of forming a pad oxide film on a semiconductor substrate, a step of forming a fine particle silicon film on the pad oxide film, A step of forming an oxidation resistant film on the silicon film, a step of selectively etching a part of the silicon film so that the oxidation resistant film remains in a predetermined region,
And a step of growing a field oxide film in a region other than the region where the oxidation resistant film remains by selective oxidation using the oxidation resistant film remaining in the above process as a mask.

The silicon film is made of amorphous silicon or microcrystalline silicon, and the oxidation resistant film is
Made of silicon nitride. In the method of forming the element isolation structure described above, the silicon film made of amorphous silicon or microcrystalline silicon functions as a barrier that suppresses the lateral growth of the bird's beak of the field oxide film. Since the silicon film has very small particles, even if the bird's beak oxidizes and grows along the particles of the silicon film, no unevenness is formed on the surface of the bird's beak. Therefore, even if an electrode material such as polysilicon is deposited in a later step and the gate electrode is patterned, the possibility that the electrode material will remain in the bird's beak is reduced. Therefore, the occurrence of short circuit of the gate electrode is suppressed, and the yield can be improved.

The thickness of the pad oxide film is preferably 500 Å or less. This is because if the pad oxide film is formed to be thick, the bird's beak of the field oxide film that will be formed in a later step grows long in the lateral direction, and as a result, the element formation region becomes shorter. The thickness of the silicon film is preferably 1500 Å or less. If the silicon film is formed thicker than 1500 Å, the bird's beak rises sharply, which may cause a clear step difference between the semiconductor substrate and the surface of the field oxide film.
That is, in order to make the bird's beak into an appropriate shape, it is preferable that the above-mentioned film thickness conditions be observed.

The silicon film is preferably thinner than the oxidation resistant film. If the silicon film is thicker than the oxidation resistant film, the bird's beak rises sharply as in the above case, a large step is generated between the semiconductor substrate and the surface of the field oxide film, and the element isolation region becomes long. As a result, the element formation region becomes shorter. As the method for forming the above-mentioned silicon film, it is preferable to adopt the LPCVD method and the deposition temperature thereof is within the range of 500 ° C to 600 ° C. This is because it is necessary to consider the difference in film forming temperature between polycrystalline silicon and fine particle silicon such as amorphous silicon or microcrystalline silicon. That is, if the deposition temperature is as high as 600 ° C. or higher, the fine particle silicon becomes polycrystalline silicon, while if it is low as 500 ° C. or lower, the reaction gas is not decomposed and the fine particle silicon does not grow.

Further, it is preferable to use silane gas as a reaction gas when the silicon film is grown by the LPCVD method. This is because silane gas has a low decomposition temperature and can be lowered in temperature.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. 1 and 2 are cross-sectional views showing a method of forming an element isolation structure according to an embodiment of the present invention in the order of steps. Referring to these drawings, in the method of forming the element isolation structure of the present embodiment, first, a pad oxide film is formed. That is, as shown in FIG. 1A, the silicon substrate 11 is heated to about 900.degree.
It oxidizes in an oxygen atmosphere to a degree. Then, a thermal oxide film (SiO ₂ ) grows, and as a result, a pad oxide film 12 is formed on the silicon substrate 11. It is preferable to form the pad oxide film 12 as thin as possible, for example, 30
The film thickness is preferably 0Å and 500Å or less.

When the pad oxide film forming step is completed,
A silicon film with very small particles is formed. That is, LP
A silicon film of fine particles is formed by using a CVD (Low Pressure Chemical Vapor Deposition) device. Specifically, the temperature of the film forming chamber is set to about 500 to 600 ° C. (for example, 580 ° C.), the silane (SiH ₄ ) gas is thermally decomposed, and the amorphous silicon film or the microcrystalline silicon film is deposited. As shown in (b), a silicon film 13 is formed on the pad oxide film 12. The film thickness of the silicon film 13 is
It is preferably 1500 Å or less, for example 1200 Å
And

When the silicon film forming step is completed, an oxidation resistant film is formed. That is, the oxidation resistant film is formed using, for example, an LPCVD apparatus. Specifically, the temperature of the film forming chamber is set to, for example, 750 ° C., and dichlorosilane (SiH
₂ Cl ₂ ) gas and ammonia (NH ₃ ) gas are caused to react with each other to deposit a silicon nitride film (Si ₃ N ₄ ).
As shown in (c), the oxidation resistant film 1 is formed on the silicon film 13.
4 is formed. The thickness of the oxidation resistant film 14 is the silicon film 1
The thickness is preferably thicker than 3, for example, 3000 Å.

When the oxidation resistant film forming step is completed, the element forming region is defined. That is, as shown in FIG. 2A, a resist 15 is patterned on the oxidation resistant film 14. This resist 15 becomes a pattern that defines a region for forming an element such as a transistor, that is, an element forming region 16. Using this resist 15 as a mask, a part of the silicon film 13 which is a portion protruding from the resist 15 is patterned by anisotropic etching (for example, RIE (Reactive Ion Etching)).

When the above process for defining the element formation region is completed,
Grow field oxide. That is, after removing the resist 15 used as a mask in the above process, selective heat treatment is performed using the oxidation resistant film 14 as a mask. Then, the pad oxide film (SiO ₂ ) 12 in the portion protruding from the oxidation resistant film 14 is thermally oxidized, and as a result, as shown in FIG.
A field oxide film 17 grows as shown in FIG. This thermal oxidation treatment is performed, for example, in a water vapor atmosphere at about 980 ° C. for about 6 hours, so that the thickness of the field oxide film 17 becomes about 8000Å. At this time, oxygen does not quickly permeate into the silicon film 13 directly below the oxidation resistant film 14, so that the silicon film 13 serves as a barrier and the field oxide film 17 does not grow much laterally. That is, the bird's beak 18 does not extend into the element formation region 16 for a long time, and a large element formation region 16 can be obtained.

After the field oxide film growth step is completed, as shown in FIG. 2C, the oxidation resistant film 14, the silicon film 13 and the pad oxide film 12 on the element forming region 16 are formed.
Are removed. As a result, the element formation region 16 is separated by the field oxide film 17. In the method of forming the element isolation structure described above, the silicon film 1 made of amorphous silicon or microcrystalline silicon is used as a barrier for suppressing the lateral growth of the bird's beak 18 of the field oxide film 17.
3 is used. Since the silicon film 13 has very small particles, as shown in FIG. 3, even if the bird's beak 18 grows by oxidation along the particles of the silicon film 13, no unevenness is formed on the surface of the bird's beak 18. Therefore, even if an electrode material such as polysilicon is deposited in a later step and the gate electrode is patterned, the possibility that the electrode material will remain on the bird's beak 18 is reduced. Therefore, the occurrence of short circuit of the gate electrode is suppressed, and the yield can be improved.

Further, as described above, the pad oxide film 12
It is preferable that the film thickness of the film is less than 500 Å or less. When the pad oxide film 12 is formed to be thick, the bird's beak 18 of the field oxide film 17 formed in a later step grows laterally long. This is because the element formation region 16 becomes shorter as a result. It is preferable that the film thickness of the silicon film 13 be 1500 Å or less. When the silicon film 13 is formed to be thicker than 1500 Å, the bird's beak 18 rises sharply and the surface of the silicon substrate 11 and the field oxide film 17 is There may be a clear step between the two. That is, in order to make the bird's beak 18 have an appropriate shape, it is preferable that the above-mentioned film thickness conditions be observed.

Further, it is preferable that the silicon film 13 is thinner than the oxidation resistant film 14 because if the silicon film 13 is thicker than the oxidation resistant film 14, the bird's beak 1
8 becomes steep and a large step is generated between the silicon substrate 11 and the surface of the field oxide film 17,
The element isolation region becomes longer. As a result, the element formation region 16
Is shortened.

As a method for forming the silicon film 13 of fine particles, the LPCVD method is adopted, and the deposition temperature is within the range of 500 ° C. to 600 ° C. because of the fine particle silicon such as amorphous silicon or microcrystalline silicon. This is because the difference in film forming temperature from that of polycrystalline silicon is taken into consideration. That is, when the deposition temperature is as high as 600 ° C. or higher, the fine particle silicon becomes polycrystalline silicon.
If the temperature is lower than 00 ° C, the source gas (silane) will not decompose,
This is because the fine particle silicon does not grow.

When the silicon film is grown by the LPCVD method, the silane gas is used as the reaction gas because the decomposition temperature of the silane gas is low and the temperature can be lowered. The present invention is not limited to the above embodiment, and many modifications and changes can be made within the scope of the present invention.

[0023]

As is apparent from the above description, according to the present invention, since the silicon film of fine particles is used as the barrier for suppressing the lateral growth of the bird's beak of the field oxide film, the surface of the bird's beak is There are no irregularities. Therefore, even if an electrode material such as polysilicon is deposited in a later step and the gate electrode is patterned, the possibility that the electrode material will remain in the bird's beak is reduced, and the occurrence of a short circuit of the gate electrode is suppressed. As a result, there is an excellent effect that the yield can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a method of forming an element isolation structure according to an embodiment of the present invention in the order of steps.

2A to 2D are cross-sectional views showing a method of forming an element isolation structure following FIG. 1 in step order.

FIG. 3 is an enlarged cross-sectional view showing a bird's beak when a field oxide film is grown.

FIG. 4 is a cross-sectional view showing a method of forming an element isolation structure by a conventional LOPOS method in the order of steps.

FIG. 5 is a cross-sectional view showing the method of forming the element isolation structure following FIG. 4, in order of steps.

FIG. 6 is an enlarged cross-sectional view showing a bird's beak when a field oxide film is grown.

FIG. 7 is a diagram showing a crater generated in a bird's beak.

[Explanation of symbols]

 11 silicon substrate 12 pad oxide film 13 silicon film 14 oxidation resistant film 15 resist 16 element formation region 17 field oxide film 18 bird's beak

Claims (7)

[Claims] 1. A step of forming a pad oxide film on a semiconductor substrate, a step of forming a silicon film of fine particles on the pad oxide film, a step of forming an oxidation resistant film on the silicon film, and a predetermined region. By the step of selectively etching a part of the silicon film so that the oxidation resistant film remains, and by selective oxidation using the oxidation resistant film remaining in the above step as a mask,
A method of forming an element isolation structure, comprising a step of growing a field oxide film in a region other than a region where an oxidation resistant film remains. 2. The method for forming an element isolation structure according to claim 1, wherein the silicon film is made of amorphous silicon or microcrystalline silicon, and the oxidation resistant film is made of silicon nitride. 3. The method for forming an element isolation structure according to claim 1, wherein the pad oxide film has a thickness of 500 Å or less. 4. The method for forming an element isolation structure according to claim 1, wherein the silicon film has a thickness of 1500 Å or less. 5. The method for forming an element isolation structure according to claim 1, wherein the silicon film is thinner than the oxidation resistant film. 6. The method of forming a silicon film as described above is LPCVD.
Method and the deposition temperature is 500 ° C to 600 ° C
The method for forming an element isolation structure according to any one of claims 1 to 5, wherein the element isolation structure is within the range. 7. The method for forming an element isolation structure according to claim 6, wherein a silane gas is used as a reaction gas when the silicon film is grown by the LPCVD method.